10 Comments

Nice graph! Perhaps a bigger issue is that average unimpaired flow appears to be < 11 maf, but total allocations are more than 16 maf/year (1.5 maf/yr for Mexico and 7.5 maf each for the upper-basin and lower-basin states). Mexico and the lower basin states already use their full allocations. As upper basin state use grows, water storage in the amazingly large Colorado R. reservoirs will diminish over time. We will blame droughts and climate change, but overallocation is a more than equal contributor to the problem. Improving allocations will have large economic benefits.

Article III(a) of the compact seems to say the former, that each basin has “the exclusive beneficial consumptive use of 7,500,000 acre-feet of water per annum”.

But then Article III(d)goes on to say that “The States of the Upper Division will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 75,000,000 acre-feet for any period of ten consecutive years” – which lower basin lawyers interpret to mean that the Upper Basin has a firm delivery obligation of 7.5maf per year, and that the upper basin is entitled to whatever’s left after that lower basin obligation is met.

Upper Basin lawyers tend to have a different interpretation – that III(d) is an obligation not to deplete, rather than an obligation to deliver, so if it’s drought or climate change doing the depletion, rather than human users, it’s not an upper basin obligation.

mahtso – Moot in the short run, yes. But the shortage sharing agreement only runs to 2026, and it only covers shortages down to elevation 1,025 in Lake Mead. After that, the above uncertainties about the Compact still matter.